Troubleshooting Guide

How to Use This Troubleshooting Guide

Most mushroom cultivation problems fall into five categories: stalled colonisation, contamination, failure to pin, aborting pins, and poor yields. Each has a short list of root causes and targeted fixes. The key is to diagnose the actual cause rather than treating symptoms — for example, adding more humidity when the real problem is CO2 buildup will make things worse, not better. Use the quick-reference table below to find your problem, then read the detailed section for the fix.

Quick-Reference Problem Table

Stalled Colonisation

Stalled colonisation is one of the most common issues for new cultivators. The jar or bag shows early white growth then stops progressing, sometimes for weeks. The three main culprits are temperature, moisture balance, and contamination that has not yet become visually obvious.

Causes and Fixes

• Too cold (below 20°C): Mycelium metabolism slows dramatically below 20°C. Target 24–26°C for colonisation. Use a heat mat, propagator, or warm cupboard. Never place jars in direct contact with a heat mat — use a towel or book to buffer the heat.
• Grain too wet: Wet grain sticks together, creates anaerobic pockets, and inhibits mycelium spread. Run the tissue test before jarring — a grain pressed against tissue paper should not leave a wet ring. If jars are already made and feel very heavy with visible condensation pooled at the bottom, there is likely too much moisture. You cannot fix over-wet grain in a sealed jar; restart with correctly hydrated grain.
• Sub-par inoculation material: Old spore syringes (over 12 months), liquid cultures that have been stored at incorrect temperatures, or contaminated LC are common causes. Test a new batch or a fresh syringe on a petri plate before inoculating new jars.
• Early contamination: If jars stall and then develop a sour smell, or any yellow or green tinge in the substrate (not on top), contamination has taken hold. Do not open the jar. Bag it inside another bag before disposal.

Contamination: Identification and Response

The ability to identify contamination quickly and respond correctly is the single most important troubleshooting skill. Different contaminants require different responses — some can be isolated around, others require immediate disposal of the entire container.

• Trichoderma (green mould): The most feared contaminant. Starts bright white (often brighter and fluffier than mycelium), then turns green as spores form. Once green, do not open the container — the spore load will contaminate everything nearby. Bag and bin immediately. Trichoderma thrives at the same temperature as mycelium and competes aggressively. Root cause is usually insufficient sterilisation time or contaminated substrate.
• Penicillium (blue-green): Looks powdery and blue-green. Common airborne contaminant. Same response as Trichoderma — bag without opening once sporulated.
• Bacterial blotch (wet rot): Appears as wet, slimy, dark patches — often grey, brown, or black — with a strongly unpleasant smell. Caused by anaerobic bacteria in overly wet substrate. Reduce moisture and increase FAE immediately. If localised on a bulk substrate surface, carefully scrape and remove the affected area with a gloved hand, then improve conditions. If the whole substrate smells foul, dispose of it.
• Cobweb mould: Fine, wispy white growth that looks like spider webs. Unlike mycelium, it is extremely fine and does not have a ropey or strand-like structure. Often occurs in high-humidity fruiting chambers. Fix: a brief fan session usually causes cobweb mould to recede, while healthy mycelium continues growing unaffected.
• Pin mould (Mucor / Rhizopus): Grey or black with tiny black dots on stalks. Extremely fast-growing. Occurs when sterilisation was inadequate or the substrate cooled too slowly before inoculation. Dispose without opening.

No Pins: Why the Mycelium Will Not Fruit

A fully white, healthy-looking substrate that refuses to produce pins is a frustrating but very common problem. Pinning requires a specific set of environmental cues — it does not happen automatically just because the substrate is colonised. Mycelium needs a reason to fruit, which in nature means detecting the approach of seasonal stress (cooling, humidity change, increased airflow).

• Temperature too high: Above 25°C, many cubensis strains will colonise happily but refuse to fruit. Lower the temperature to 20–23°C and maintain it consistently. A brief cold shock — moving the substrate to a cooler location (15–18°C) for 12–24 hours — can trigger pinning in stubborn tubs.
• CO2 too high: CO2 above 1000 ppm suppresses pinning. This is the most commonly overlooked cause of no-pin situations. Increase fresh air exchange: fan the chamber 4–6 times per day with a handheld fan or lid fan, or enlarge polyfill ports on monotubs. Target CO2 below 800 ppm during fruiting.
• Substrate too dry: If the surface has dried out, pins cannot initiate. Re-mist the walls and surface with a fine atomiser and allow conditions to stabilise for 48 hours before deciding the tub has failed to pin.
• Overlay: A thick mycelium mat on the surface prevents pins from reaching the surface. Scrape gently with a sterile fork in parallel lines, apply a thin fresh casing layer, and resume fruiting conditions.

Aborting Pins and Poor Yields

Pin abortion — where pins initiate correctly but then turn yellow, shrivel, and die before reaching harvest size — is usually an environmental stability problem. The mycelium is sensitive to sudden changes during the fruiting phase. Common causes include:

• Temperature swings: Drops or rises of more than 3–4°C over a short period cause widespread pin abortion. Avoid placing fruiting chambers near windows, vents, or air conditioning units. A stable 21–23°C throughout the day is far more important than hitting an exact target temperature.
• Excessive direct misting: Spraying water directly onto developing pins saturates the cap surface and can cause bacterial spotting or physical damage. Always mist the walls of the fruiting chamber, not the substrate or pins directly.
• Humidity crash: If the chamber dries below 70% RH, early pins abort rapidly. Check the seal of your fruiting chamber and mist more frequently, or add a humidity controller with an ultrasonic humidifier.
• Low substrate moisture after flush 1: The substrate loses substantial water weight with each flush. After harvesting the first flush, rehydrate by dunking the substrate in cold water for 12–24 hours (weigh it down to keep it submerged), drain for 30 minutes, then return to fruiting conditions. This is the single most effective technique for improving second and third flush yields.